This invention relates generally to an improvement in downhole tools and to methods of using the same. This invention relates more particularly, but not by way of limitation, to a pressure balanced tubular spring slip-joint and jar which eliminates the need for conventional telescoping slip-joints with sliding seals.
In drilling and testing a well, downhole tools are used to monitor downhole conditions, such as temperature and pressure, to obtain information which is helpful in evaluating the nature of the well, such as whether the well is likely to produce hydrocarbons. One particular condition which is preferably monitored is reservoir pressure measured over periods of time during which the well is alternately allowed to flow and prevented from flowing. This condition may be determined by means of a drill stem test which can be conducted utilizing techniques known in the art.
One such technique using an improved downhole tool for drill stem testing is described in copending U.S. application Ser. No. 480,981, assigned to the assignee of the present application and hereby incorporated herein by reference. The downhole tool disclosed in the aforesaid copending application is constructed to be utilized without the need of any downhole electrical controls in placing the tool in an operating position in a well, in removing it therefrom, or in mechanically opening and closing a valve of the tool. The tool also includes jarring means for assisting in the mechanical implacement and extraction of the tool, and is also constructed so that it is of a size which makes it relatively easy to transport and handle. The preferred embodiment of the tool is particularly constructed to sense reservoir pressures and provide electrical signals to the surface for generating real-time readouts of the pressure magnitudes, and includes a relatively easily removable protective housing for containing a sensor which senses the desired downhole condition.
The method of using the aforesaid tool broadly includes lowering the probe part of the tool into the well on a cable whose movement is controlled by a suitable hoist means located at the surface of the well. The probe is lowered into the well until a connector thereon suitably engages protuberances of slide means on the portion of the tool incorporated in the tool string. The cable is then withdrawn from the well to raise the probe so that the connector locks with the protuberances whereby further lifting of the probe moves the slide means upward against biasing means to the tool-actuated position. Once the tool has performed its function in the tool-actuated position, the cable is lowered so that the probe descends into the well whereby the connector unlocks from the protuberances. The cable is then raised so that the probe is lifted out of the well. To assist in the engagement or removal of the connector and the protuberances, the cable can be raised a short distance to activate the jarring means and then released to allow the jarring means to slam into the housing with a force impulse. The jarring means can also be used so that the force impulse is applied by a quick upward movement of, rather than a release of, the cable.
While this tool is an improvement over the prior art, it suffers from several major disadvantages. First, with the sensor device located in the bottom portion of the probe, lengthy electrical conductors with several connections are required to connect the sensor device to the wireline head at the top of the tool, increasing the possibility of data transmission failure. Furthermore, the location of the sensor device in the bottom of the probe makes it very vulnerable to the shocks the probe may encounter on its trip down the well bore, and makes it and its attendant electrical part of the connections an integral part of the jarring means, again contributing to the possibility of electrical failure due to the lengthy conductors and multiple connectors employed. In addition, the location of the sensor device in the probe makes disassembly thereof necessary for sensor device replacement. Finally, locating the sensor device within the lower portion of the probe reduces the force which can be applied in a downward direction by the jarring means, without the addition of sinker bars or other weighting means to the wireline head, making the probe much more difficult to handle and placing greater strain on the wireline.